Electroplating



United States 2,839,457 ELECTROPLATING No Drawing. Application November 16, 1956 Serial No. 622,530

Claims. (Cl. 204-49) This invention relates to electroplating and, more particularly, to electrodepositing nickel from an aqueous acidic nickel plating bath. The invention is based on our discovery that aromatic N-oxide compounds, when incorporated in a nickel electroplating bath, particularly in conjunction with various sulfo-oxygen compounds, are capable of promoting the formation of excellent bright and ductile electrodeposits of nickel over a Wide current density range.

The electrodeposition of nickel from a plating bath containing a sulfo-oxygen carrier brightener additive does not produce fully bright deposits. Moreover, such brightness as is produced using these agents is obtained over only a limited current density range. When, however, a small quantity of an aromatic N-oxide compound is incorporated in the plating bath together with a sulfooxygen compound, the brightening capacity of the bath is extended, and the electrodeposit is ductile and bright over a very wide current density range.

These aromatic N-oxide compounds possess, as their common structural feature, the presence of a highly polar nitrogen-oxygen bond, having the following strutural formula:

f 9 Only relatively small quantities of the aromatic N-oxide compounds are required in the plating bath, especially when they are used in conjunction with a sulfo-oxygen carrier brightener, for we have found that the highly polar nitrogen-oxygen bond appears to exert a pronounced synergistic efiect on the brightening capacity of the sulfooxygen compound. In general, concentrations of the aromatic N-oxide compounds as low as 0.01 gram per liter are effective. There appears to be no critical upper limit on the concentration of the N-oxide compound, but there is no advantage in using more thanl gram per liter, and in most plating 'baths substantially full benefit of its presence is achieved with 0.5, gram per liter or less.

Any aromatic N-oxide compound which is capable of being dissolved by acid and does not undergo decomposition upon protonation may be selected for inclusion in the plating solution. We have obtained particularly satisfactory results by using a pyridine-N-oxide of the group consisting of pyridine-N-oxide, Z-picolineddoxide, 3- picoline-N-oxide, 4--picoline-N-oxide, 2,4-lutidine-l l-oxide, -2,6-lutidine-N-oxide, 2,4,6-trimethylpyridine-N-oxide,

Z-ethylpyridine-N-oxide, 3-ethylpyridine-N-oxide, and 4- ethylpyridine-N-oxide.

A preferred process according to this invention for producing bright nickel deposits comprises electrodeposiling nickel from an aqueous acidic solution of at least one nickel salt, in which there is dissolved from about 0.02 to about 0.5 gram per liter of a pyridine-N-oxide compound having the formula in which R R and R are substituents selected from the group consisting of hydrogen, methyl, ethyl and propyl radicals, and from about A to about grams per liter of a water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

Preparation of the unsaturated N-oxide compounds may be accomplished by direct oxidation of the corresponding free base. The pyridine-N-oxide compounds generally are prepared by using a vigorous oxidizing reagent, such as ozone (0 or the peroxy acids, such as peracetic acid, perbenzoic acid, and monoperphthalic acid. Examples of the pyridine-N-oxide compounds which may be used successfully in embodiments of this invention are listed in Table I. Although these unsaturated N-oxide compounds may be used in concentrations as high as 1 gram per liter, there is no particular advantage to be gained from the higher concentrations, and they are preferably used in the range of concentrations from about 0.2 to about 0.5 gram per liter.

TABLE I Pyridine-N-oxide compounds Rt R Compound R R R3 R4 R5 Pyridine-Noxide H H H H H 2-Picoline-l\ -0xide CH H H H H 3-Picolme-N-0xide H CH3 H H H t-Picoline-lfi -oxlde H H CH3 H H 2-Ethylpyricliue-N-oxide. I CzHls H H H H 3-H) thylpyridine-N-oxide H 0 H; H H H 4-Ethylpyridine-N-oxide H H 0 H; H H l-Isopropyl ayrid lne-N-oxide H H 0 11 H H 2,4-Lutidine-i I-oxide OH; H OH; H H 2,6-Lutidine-N-oxide- CH3 H H H OH; 2-Methyl-5-ethylpyridl1ie- IRE-(Ede -.1 i CH9 H H CzHs H 2- e y -4-iospropy pyr dineN-oxide OH; H CaH- H H 2-Methyl-4-ethylpyr1dlne- N -oxide CH: H C H H H 4-Methyl- N-OXl H ogHs CH5 H H 2,4,6-T

oxide CH H OH; H CH Z-Ethyl-Z-l, 5-din1ethylpyridine-N oxide OgHs CH H OH; H

The compounds listed in Table II are examples of sulfooxygen compounds which, when used in the plating bath in combination with the unsaturated N-oxide compounds, extend the current density range over which the formation of ductile and bright nickel electrodeposits may be obtained. These sulfa-oxygen compounds may be used over a very wide range of concentrations to 80 grams per liter) but perierably are used in an amount in the range from about 1 to about 20 grams per liter. W

3 TABLE 11 Organic sulfa-oxygen compounds 1) Unsaturated aliphatic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof: 5

Sodium vinyl sulfonate, H C=CHSO Na Sodium allyl sulfonate, H C=CHCH SO Na (2) Mononuclear aromatic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

rn-Benzene disulfonic acid, C I-I (SO H) Sodium m-benzene disulfonate, C H (SO Na) Nickel m-benzene disulfonate, C H (SO Ni o-Sulfobenzoic acid monoammonium salt,

HOOCC H SO NH 1-amino-2,5-benzene disulfonic acid, H NC H (SO H) o-aminobenzene sulfonic acid, H NC H SO H (3) Mononuclear aromatic sulfinic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Sodium benzene sulfinate, C H SO Na Sodium p-toluene sulfinate, CH C H SO Na (4) Mononuclear aromatic sulfonamides and sulfonimides:

Benzene sulfonamide, C H SO NH p-Toluene sulfonamide, CH C H SO NH o-Sulfobenzoic imide,

CuH CONHSOg Benzyl sulfonamide, C H CH S0 NH Benzene sulfhydroxamic acid, C H SO NHOH N,N-dimethyl-p-toluene sulfonamide,

CH C H SO N (CH 3 N,N-dicarboxyethyl benzene sulfonamide,

(5) Binuclear aromatic sulfonic acids, and alkali metal,

ammonium, magnesium, and nickel salts thereof:

Z-naphthalene monosulfonic acid, C H SO H 1,5- or 2,7-naphthalene disulfonic acid, C H (SO H) Nickel 1,5- or 2,7-naphthalene disulfonate,

Naphthalene trisulfonic acid, C H (SO H) Sodium naphthalene trisulfonate, C H (SO Na) Diphenyl p,p-disulfonic acid, HSO C H.,,C H SO H Z-naphthol-B,6-disulfonic acid, HOC H (SO H) Sodium 2-naphthol-3,6-disulfonate, HOC I-I (S0 Na) l-naphthylamine-3,6,3-trisulfonic acid,

(6) Heterocyclic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Thiophene sulfonic acid, C H S.SO H Sodium thiophene sulfonate, C H S.SO Na 2-(4-pyridyl)ethyl sulfonic acid, C H N.C H SG H I clectrodeposition from any aqueous acidic plating solution of one or more nickel salts.

To illustrate the applicability of using the pyridine-N- oxide compounds in different nickel electroplating baths under a variety of conditions, Table III lists the basic compositions of several types of plating baths which were employed in carrying out the examples of the invention that are set forth below.

TABLE III Bat/z concentrations in grams per liter Bath A Bath B Bath 0 Nickel sulfate 300 Nickel chloride. Nickel suliamate. Nickel fluoborate. Boric acid In each of the following examples of the invention, the electrodeposit was formed in a Hull test cell on brass cathodes so that the effect of a wide range of current densities could be observed. The pH of the bath was adjusted to about 3.5 in each case, and the electrodeposit was formed at a temperature of 50 C. Mild agitation of the bath was provided in each case.

Table IV summarizes the concentrations of addition agents used in eleven examples of the invention based on the use of a standard Watts plating solution (bath A) containing varying concentrations of representativesulfooxygen compounds and pyridine-N-oxide compounds. An exceptionally bright electrodeposit was formed in each case.

TABLE IV Effect of pyridine-N-oxide compounds on Watts nickel plating solution (bath A) Brlghtener Additives (Grams/Liter) 1 2 3 A. Sulfo-Oxygen Compounds:

Sodium naphthalened, 3, G-trisulfonate Sodium naphthalene-2, 7-disul fonate Benzene sulfonic acid B. Pyridine-N-oxide Compounds:-

Py'ridine-N-oxide 2-]?icoline-N-oxlde 4-Plcollne-N- Excellent results were also obtained when the pyridine-N-oxides were used in a nickel sulfamate bath (Bath B) containing 15 grams per liter of sodium naphthalene-1,3,6-trisulfonate and 0.16 gram per liter of pyridine-N-oxide. The deposit formed from such bath in at Hull test cell Was bright over a very wide current density range. Increasing the pyridine-N-oxide to 0.32 gram per liter did not substantially increase the brightness.

A nickel electrodeposit formed on the test panel from a nickel fluoborate bath (bath C) containing 15 grams per liter of sodium naphthalene-1,3,6-trisulfonate, but no pyridine-N-oxide compound, was hazy and only semibright. Upon the addition of 0.16 gram per liter of pyridine-N-oxide to this bath, the deposit was bright over the entire current density range. Similarly, bright deposits were obtained from fiuoborate baths containing 15 grams per liter of sodium naphthalene-1,3,6-trisulfonate and from 0.16 to 0.26 gram per liter of 2,6- lutidine-N-oxide.

We claim:

1. The process for producing bright nickel deposits which comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.01 to about 1 gram per liter of an aromatic N-oxide compound possessing a polar nitrogen-oxygen bond having the structural formula in which the nitrogen atom forms part of a heterocyclic ring, and from about A to about 80 grams per liter of a Water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

2. The process for producing bright nickel deposits which comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.02 to about 0.5 gram per liter of a pyridine-N-oxide of the group consisting of pyridine- N-oxide, Z-picoline N oxide, 3-picoline-N-oxide, 4- picoline-N-oxide, 2,4 lutidine N oxide, 2,6-lutidine- N-oxide, 2,4,6-trimethylpyridine N oxide, Z-ethylpyridine-N-oxide, B-ethylpyridine N oxide, and 4- ethylpyridine-N-oxide, and from about A to about 80 grams per liter of a water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sul finic acids, the alkali-metal, magnesium, ammonium, and nickel salts of said acids, and mononucleur aromatic sul fonamides and sulfonimides.

3. The process for producing bright nickel deposits which comprises electrodepositing nickel from an aqueous acid solution of at least one nickel salt in which there is dissolved from about 0.01 to about 1 gram per liter of a pyridine-N-oxide having the formula in which R R and R are substituents selected from the group consisting of hydrogen, methyl, ethyl, and propyl radicals, and from about /4 to about grams per liter of a Water-soluble sulfo-ozygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mcnonuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

4. An aqueous acidic nickel electroplatingbath in which there is dissolved from about 0.02 to about 0.5 gram per liter of a pyridine-N-oxide having the formula in which R R and R are substituents selected from the group consisting of hydrogen, methyl, ethyl, and propyl radicals, and from about /4 to about 80 grams per liter of a Water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuelear aromatic sulfinic acids, the alkali-metal, magnesium, ammonium, and

nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

5. An aqueous acidic nickel electroplating bath in Which there is dissolved from about 0.01 to about 1 gram per liter of a pyridine-N-oxide of the group consisting of pyridine-N-oxide, Z-picoline -N-oxide, 3- picoline-N-oxide, 4- picoline N oxide, 2,4lutidine-N- oxide, 2,6-lutidine N oxide, 2,4,6-trimethylpyridine- N-oxide, 2-ethylpyridine N oxide, B-ethylpyridine-N- oxide, and 4-ethylpyridine-N-oxide, and from about A. to about 80 grams per liter of a water-soluble sulfooxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic snlfinic acids, the alkali-metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sultonimides.

References Cited in the file of this patent UNITED STATES PATENTS 2,644,788 Shenk Q July 7, 1953 2,644,789 Shenk July 7, 1953 2,647,866 Brown Aug. 4, 1953 2,658,867 Little Nov. 10, 1953 

1. THE PROCESS FOR PRODUCING BRIGHT NICKEL DEPOSITS WHICH COMPRISES ELECTRODEPOSITING NICKEL FROM AN AQUEOUS ACIDIC SOLUTION OF AT LEAST ONE NICKEL SALT IN WHICH THERE IS DISSOLVED FROM ABOUT 0.01 TO ABOUT 1 GRAM PER LITER OF AN AROMATIC N-OXIDE COMPOUND POSSESSING A POLAR NITROGEN-OXYGEN BOND HAVING THE STRUCTURAL FORMULA 